In the conventional power supplier, a series of rectifier, filter and clamp circuit are used to convert the power into DC output at specific voltage for providing to equipments, like computer. However, this architecture has a low efficiency and always causes at least 40% electricity loss so that it is hard to provide precise current or voltage. Then, owing to technical advancement, electronic components are used to modulate high-frequency switch element and duty cycle so that the main product of power supplier in the market can have the efficiency up to 80%. The basic method for using PMW (Pulse Width Modulation) to control duty cycle is to utilize an IC with built-in PWM circuit. However, since the price of IC is expensive, other low cost circuit architectures are developed for instead.
For example, a pulse control constituted by latch circuit is disclosed in R.O.C Patent Publication 501830 “improved switch power supplier”, wherein the pulse width modulation circuit (44) namely employs a latch circuit to be the switch for substituting the pulse controller chip to control the duty cycle of back-end assistant power source. But, this method still has inconvincible problems. First, the conduction of latch circuit relies on the pulse from the frontend circuit so that the latch circuit lacks of suitable bias voltage for maintaining the conduction, and after the latch circuit is conducted, it will only transmit the pulse signal to the back-end MOSFET, which controls the output of the assistant power source, so that the MOSFET can only maintain the conduction through gate capacitor after being triggered so as to cause insufficient conducting amount. Therefore, in other words, the MOSFET only maintains in the threshold range of “just enough for conduction” so that the stability is insufficient and the MOSFET might be easily error triggered due to the floating gate potential. On the other hand, since temperature variation may vary the current conducting amount of electronic component and the single latch circuit lacks of temperature compensating mechanism, the temperature variation may cause the electronic component to generate leakage current and also the latch circuit or MOSFET to be triggered erroneously; further, because the latch circuit architecture does not include surge noise interference device, it is also easy to cause error trigger; and besides, the latch circuit has a mechanism for limiting maximum duty cycle which also causes the assistant power system to become unstable when heavy load.
Consequently, although replacing the pulse controller chip by one latch circuit can reduce production cost, the latch circuit still has some problems need to solve.